An engine of a vehicle may include a cylinder having a direct injection fuel injector and a port injection fuel injector. The port injection fuel injector may be supplied with gasoline only from a first fuel storage tank and the direct injection fuel injector may be supplied with ethanol only from a second fuel storage tank. This engine configuration is one example of what may be referred to as an ethanol boosted system which may be used to enhance engine operating efficiency and improve fuel economy performance. For example, under some conditions, the port injection fuel injector may inject a reduced amount of gasoline and the direct injection fuel injector may inject ethanol to abate engine knock which otherwise would be caused by operation at increased boost levels and/or compression ratios.
The inventors herein have recognized issues with the above approach. In particular, in the above engine configuration, at cold engine start start-up, an emissions control device of the vehicle may be at a temperature below an operational light-off temperature, and thus quick heating of the emissions control device may be desired to control vehicle emissions. However, at a cold engine start-up condition, direct injection of ethanol for combustion may result in unstable combustion or modest heat generation since ethanol may not vaporize at cold temperatures. Likewise, port injected gasoline for combustion may produce modest heat generation resulting in slower emissions control device warm-up.
At least some of the above issues may be overcome, in one approach, by a method of controlling fuel supplied to an engine of a vehicle, the vehicle including a first fuel storage tank to store a first type of fuel, a second fuel storage tank to store a second type of fuel, and an emissions control device, the engine including at least one cylinder having a direct injection fuel injector being selectively supplied with the first type of fuel from the first fuel storage tank and the second type of fuel from the second fuel storage tank, the method comprising: supplying the first type of fuel from the first fuel storage tank to the direct injection fuel injector in response an engine start condition of the vehicle; and supplying the second type of fuel from the second fuel storage tank to the direct injection fuel injector, in response to an increase in engine output exceeding a threshold increase or a temperature of the emissions control device exceeding a threshold temperature.
In one example, gasoline is supplied to the direct injection fuel injector at cold engine start-up and the direct injection fuel injector performs mild stratified injections of gasoline. In particular, at engine startup, gasoline may be preferable for direct injection over ethanol because gasoline vaporizes at cooler temperatures relative to ethanol. The vaporized gasoline may form a stratified mixture of air and fuel providing enhanced combustion stability that enables additional spark retard for increased exhaust heat. Thus, by supplying stratified gasoline via the direct injector at engine startup exhaust heat generation may be increased. In this way, an emissions control device may be heated to a light-off temperature in a quick manner.
Furthermore, upon the emissions control device reaching the light-off temperature, gasoline is no longer needed for heating of the emissions control device, thus ethanol is supplied to the direct injection fuel injector. Also, if the engine load increases to a substantially high load prior to the emissions control device reaching the light-off temperature, ethanol may be supplied to the direct injection fuel injector for knock suppression purposes. In particular, the directly injected ethanol may provide substantial charge cooling due to the higher heat of vaporization of ethanol resulting in suppression of engine knock. By suppressing engine knock, engine output may be increased without substantial engine degradation. In this way, the operating efficiency of the engine may be improved.
Accordingly, the above described approach may supply gasoline to the direct injection fuel injectors for improved emissions control device heating at engine startup. Then, the approach may transition to supplying ethanol to the direct injection fuel injectors to suppress engine knock and increase output. In this way, the vehicle emission may be reduced and operating efficiency may be increased.